Asphalt is typically produced by heat drying virgin asphalt aggregate and by adding to it and mixing with it liquid asphalt cement, fillers and other additives, often including recycled asphalt pavement. Often times, asphalt is also made by drying virgin asphalt aggregate and moving it to a batch plant tower for batch mixing with the asphalt and other additives.
Prior art systems, such as the one disclosed in U.S. Pat. No. 4,892,411, entitled ASPHALT MIXER APPARATUS AND METHOD, disclose counterflow Drum Mix type systems. In these systems, the plants produce either a mixture of recycled asphalt and virgin materials or of virgin materials only. Two concentric drums, one being for drying the materials and one being for mixing the materials, are used. Aggregates are put into the first, drying rotating drum and the materials move in a direction toward the second, mixing rotating drum. A burner is mounted behind the second drum and extends through this drum to the first drum for directing a flame into the first drum. The materials moving in the first drum move towards the flame and under the influence of the heat are dried. The aggregate then moves into the second drum which mixes it with liquid asphalt, fines and recycled asphalt materials. Although such a system produces asphalt products, it and others can be inefficient and damaging on equipment. For example, by having the burner extend through the second cylinder, the mixing chamber must be extremely large. And, the added size requires more power to drive. Further, by having the drums abutting one another, access to the inlet opening of the second, mixer drum is difficult. Thus, repairs and monitoring, and even the introduction of materials, can be difficult. Further, this arrangement requires the modification of a standard industrial burner, such as by attachment of an extension, to reach into the first cylinder.